The intensity of the electric field required to keep a water drop of radius $10^{-5} \, cm$ just suspended in air when charged with one electron is approximately:

$A$ circular disc of radius $R$ and thickness $\frac{R}{6}$ has a moment of inertia $I$ about an axis passing through its center and perpendicular to its plane. It is melted and recast into a solid sphere. The moment of inertia of this sphere about its diameter is:

Pure line breed refers to

In order to oxidize a mixture of one mole of each of $FeC_2O_4$,$Fe_2(C_2O_4)_3$,$FeSO_4$,and $Fe_2(SO_4)_3$ in an acidic medium,the number of moles of $KMnO_4$ required is:

$A$ vertical pole subtends an angle $\tan ^{-1}\left(\frac{1}{2}\right)$ at a point $P$ on the ground. If the angles subtended by the upper half and the lower half of the pole at $P$ are respectively $\alpha$ and $\beta$,then $(\tan \alpha, \tan \beta)$ is equal to

Read the following five statements and answer the question.
$(a)$ In $Equisetum$ the female gametophyte is retained on the parent sporophyte.
$(b)$ In $Ginkgo$ male gametophyte is not independent.
$(c)$ The sporophyte in $Riccia$ is more developed than that in $Polytrichum$.
$(d)$ Sexual reproduction in $Volvox$ is isogamous.
$(e)$ The spores of slime molds lack cell walls.
How many of the above statements are correct?